TITLE:   GCN CIRCULAR
NUMBER:  33352
SUBJECT: GRB 230220A: MAXI/GSC detection
DATE:    23/02/20 10:29:08 GMT
FROM:    Hitoshi Negoro at Nihon U  <negoro.hitoshi@nihon-u.ac.jp>

S. Nawa (Chuo U.), H. Negoro, M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.), 
T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), 
T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), 
Y. Tsuboi, J. Kohara, S. Urabe, N. Nemoto (Chuo U.), M. Shidatsu, M. Iwasaki (Ehime U.),
N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), 
S. Nakahira,  S. Ueno, H. Tomida, M. Ishikawa,  T. Kurihara (JAXA), 
Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba, Y. Nakatani (Kyoto U.), 
M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. Hagiwara, Y. Umeki (Miyazaki U.), 
K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC), W. Iwakiri (Chiba U.) 
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source 
at 08:55:58 UT on 20  Feb 2023. Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (346.565 deg, 18.607 deg) = (23 06 15, +18 36 25) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.22 deg and 0.19 deg, respectively.
The roll angle of long axis from the north direction is 153.0 deg counterclockwise.
Without assumptions on the source constancy, we obtain a rectangular error box 
for the transient source with the following corners.
(196.900, -21.911) deg = (13 07 36, -21 54 39) (J2000)
(196.998, -22.143) deg = (13 07 59, -22 08 34) (J2000)
(198.373, -21.637) deg = (13 13 29, -21 38 13) (J2000)
(198.273, -21.406) deg = (13 13 05, -21 24 21) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 182 +- 28 mCrab (4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 07:22 UT with an upper limit of 20 mCrab.